Cardiovascular disease, including atherosclerosis, is a leading cause of death in the U.S. A number of methods and devices for treating this disease in vessels of the heart and throughout the vasculature have been developed, including a broad array of catheters and minimally invasive methods for using them. Catheter-based delivery systems are routinely used to introduce stents and other medical devices into the cardiovascular system for both therapeutic and diagnostic purposes.
Typically, the catheter is inserted into the vascular system percutaneously through an artery, such as the femoral, jugular, or radial artery. The catheter is threaded through the vascular system until the distal end of the catheter is adjacent to the treatment site. The position of the catheter end may be determined by common visualization methods such as fluoroscopy or ultrasound. To reach treatment sites distant from the insertion site, guiding catheters are typically used to provide a tubular conduit, open at both ends, and through which smaller devices are passed. Guiding catheters have as large a through-lumen as possible, given the constraints of a nominal outer diameter, e.g. 6 French (2.00 mm) and a wall thickness sufficient to provide the required functional properties.
In order to perform well, a guiding catheter must have sufficient columnar strength and rigidity so that it can be pushed through the vasculature of the patient without bending back on itself or kinking. However, if it is too stiff, it may cause damage to blood vessel walls. At the same time, the catheter must be sufficiently flexible so that it can follow a winding, sometimes tortuous, path through the patient's vasculature. In order to balance the need for both flexibility and columnar strength, catheters are frequently constructed to have a relatively rigid proximal section and a more flexible distal section. Such a balanced combination also provides a catheter with good steerability, which is the ability to transmit substantially all rotational inputs from the proximal end to the distal end. Controlled rotation of the distal end of a catheter is useful for directing catheters that have pre-formed or curved distal ends.
Known catheter designs attempt to achieve this balance of physical properties by using support layers of braided filaments combined with elongate axially oriented filaments within the wall of the catheter. A braided support layer provides resistance to crushing, kinking or radial expansion from internal pressure, while adding substantial torsional stiffness, and may add bending stiffness to the catheter. Elongate axial filaments increase tensile modulus of the assembly and also provide bending stiffness to the catheter.
The braided material is positioned along at least a portion of the length of the catheter. The axial filaments are also positioned along the length of the catheter, running alongside or within the braided layer. One drawback to a catheter having both a braided layer and an axial layer is that the catheter may be too stiff to traverse the tortuous vascular pathways. Another drawback to having a catheter with a multi-layer support layer is the added cost. Yet another drawback of the multi-layer support is that the multiple layers may create undesirable additional thickness of the catheter wall, especially in those catheters having the multi-layer support disposed between an outer polymeric bonding layer and an inner polymeric (liner) layer.
One solution to the undesirable increase in thickness of the catheter wall was to produce a liner-less catheter, such as catheter 10 illustrated in FIG. 1. FIG. 1 shows a longitudinal cross section of a portion of a liner-less catheter 10. Catheter 10 includes an outer polymeric layer 15 and a braided reinforcing (support) layer 20 composed of flat wire filaments 25. One drawback to a liner-less guiding catheter is that in use the treating clinician often feels a disconcerting “zipper effect” as a treating device is advanced through the catheter. This zipper effect is due to the device traversing the uneven inner surface of the support layer.
It would be desirable, therefore, to provide a catheter that has the advantages of both braided and axial support layers while overcoming these and other disadvantages.